Thixotropy of Solder Paste Impacts Repeatability and Reproducibility of Rheometric Results

摘要

The aforementioned sample preparation method in conjunction with the use of rheometric indexes that have been proposed before, yields significantly more accurate and reproducible results, and also saves time and money. The procedure requires approximately 5 to 10 minutes for the lab technician to set it up. The rheometer phase requires no more than 16 minutes to produce the final numbers. As proposed before, we are able to determine rheometric slump and tackiness as well as index for speed and temperature sensitivity. All output data is measured, smoothed, interpolated and calculated automatically. With the sample preparation routine we can even determine rheometric tackiness of the solder paste after time intervals like 1,2,4,8,16 hours as we print the test coupons and leave them in the dessicator for the duration as required by the test specification.Whereas the ISO-TS 16949 Instruction Manual for the Parts Production Approval Process (PPAP), Fourth Edition, March 2006, Section F9, page 46, acknowledges the larger measurement variability for properties (such as viscosity) in the process industry, accounting in some cases for 50% or more of the total variation, we are able to certify variations of maximum 5% with the recent enhancements to our rheometric techniques as described in this paper. A new industry standard based on indexes such as i_t,i_v, i_(vt) and other Theological parameters including slump and tackiness would finally put an end to confusion and discussions about all kinds of test conditions regarding viscosity. It would also end the hassle associated with control items such as slump stencils, tackiness probe alignment and other issues. Moreover, this test provides much more useful and reliable information about the printing properties, under varying operating conditions, of a solder paste to the user. Initially, one might be concerned with the apparent higher initial investment in instrumentation, which also requires a well-trained lab technician to operate and correctly interpret the results. However, many users never measure viscosity and other rheological properties, and rely on certification by the vendor, which may not always be reliable. The abovementioned procedure provides a solid level of assurance to the user. It is therefore important for the user to demand a certificate of compliance from the paste vendor regarding the testing of aforementioned rheological parameters. In modern business practice, transparency is a key word. Therefore, paste vendors should allow customers to audit their SPC data under certain conditions. 1. A Simpler Approach to Cost-Effective Solder Paste Testing, Ineke van Tiggelen-Aarden, Proceedings APEX-2003 Conference 2. Ein kostenguenstiger Methode fuer Qualitaetsicherung, Ineke van Tiggelen-Aarden, Productronic, October & November 2003 3. Correlation of Malcom Spiral Viscometer vs. Brookfield T-bar Spindle Viscometer, Kantesh Dos, Austin American Technology 4. A Fast, Precise and Reproducible QC-Rheometry Routine for Solder Paste, Ineke van Tiggelen-Aarden, Proceedings APEX-2004 Conference 5. The Complex Viscosity is determined by sinusoidal shear loads through oscillatory testing and therefore noted with an asterisk to indicate the complex form, and thus distinguish it from a viscosity value that has been established by rotational testing. 6. Chrysler, Ford & GM: "Parts Production Approval Process -^sPPAP", Reference Manual AIAG, Troy, Michigan 2006.